1. Field of the Invention
The present invention relates to an automotive heat exchanging system which is applied to a motor vehicle with an automatic transmission.
2. Description of the Related Art
In general, the automotive heat exchanging system of this kind comprises a radiator mounted in the front of a vehicle, an electric fan located behind the radiator, a shroud covering from a periphery of the radiator to a periphery of the fan and forming an air passage in the shroud for guiding air toward an engine to get rid of excess engine heat, a shutter driven by an actuator and installed in front of the radiator, and a controller which controls the actuator to move the shutter between a full open position and a closed position to adjust an amount of airflow for cooling the engine according to a predetermined condition.
A conventional automotive heat exchanging system constructed as above is disclosed in, for example, Japanese patent laying-open publication Tokkaihei 5-133226. This system further comprises an oil pump to discharge a pressurized oil, a control valve modulating the oil pressure from the oil pump according to heat load of the engine, and an oil motor driven by the oil pressure supplied from the control valve. In this system, the pressure modulated oil is supplied to the oil motor for driving the fan and to the actuator for moving the shutter to change its opening.
Another conventional automotive heat exchanging system constructed as above is disclosed in, for example, Japanese patent laying-open publication Tokkai 2000-130167. This system has two shutters; a first shutter located in front of the area covered by the shroud, and a second shutter located in front of the area uncovered by the shroud. In this system, the second shutter is controlled to close when a vehicle speed is at most a predetermined speed, and the first shutter is controlled to open when a temperature of a coolant in the radiator is at most a predetermined temperature.
Incidentally, the automotive heat exchanging system has a close relationship to fuel consumption of an engine, for it effects cooling and warming up the engine and an automatic transmission.
The engine discharges exhaust gas in the air through an exhaust system including an exhaust pipe, a muffler, and a catalyst converter. The exhaust gas from the engine includes pollutant components, which is reduced by the catalyst converter.
The catalytic converter is activated when its temperature is more than a certain temperature, while its catalytic activity is reduced when it is not. This results in that as the time for engine running at low engine temperature, during a warm-up phase of the engine after engine-starting, becomes longer, it brings more fuel consumption, for a rich fuel-air mixture is supplied to the engine to burn at high temperature and activate the catalytic converter by high temperature gas.
In the automatic transmission, a lock-up clutch is used for engaging an impeller and a turbine of a torque converter to reduce the fuel consumption. Recently, attempts to engage the lock-up clutch at as low a vehicle speed as possible, for example at 40 Km/h, are made for less fuel consumption. The lock-up at low speed, however, sometimes brings unwilled engine stop especially at low automatic transmission oil temperature, for an oil in the automatic transmission has a high viscosity at low temperature.
At present, the lock-up is controlled based on an engine temperature, and disengaged in order to avoid engine stop when an engine temperature is lower than a predetermined engine temperature.
This brings a delay in raising the engine temperature, causing an increase in the fuel consumption. Besides, a delay of lock-up during warm-up after engine-starting is created because the engine temperature and the automatic transmission oil temperature do not always correspond to each other.
This means that it is desirable to prevent air from passing through the radiator and from bypassing the radiator to flow toward the engine and the automatic transmission at low oil temperature after engine-starting.
The above known conventional automotive heat exchanging systems, however, encounter such a problem that they are not sufficient for reducing fuel consumption when an oil temperature of an automatic transmission is low after engine-starting.
In the above mentioned conventional systems, the shutter is located in front of the radiator covered by the shroud, which causes air to bypass the shutter while flowing toward the engine and the automatic transmission to cool them. In addition, in the systems, the shutter is controlled based on the engine temperature, which does not always correspond to the automatic transmission oil temperature, which fails less fuel consumption, because it takes a long time to warm up the automatic transmission oil.
It is, therefore, an object of the present invention to provide an automotive heat exchanging system which can prevent air from flowing through a shroud toward an automatic transmission and from bypassing a shutter and flowing toward the automatic transmission for speeding up an automatic oil temperature to reduce fuel consumption when the oil temperature of the automatic transmission is low.